In testing 2.6.27-rc1, I found that p54usb caused my machine to freeze. A fewtimes, I was able to use the KDE system status applet to see that the system wasusing essentially 100% of the CPU's. One other time, the system responded a little - enough for me to see tha wpa_supplicant was consuming 100% of the my AMD Turion 64 X2 running an x86_64 kernel. From bisection, the problem is due to